Porous silicon forms by generating pores in the nanometer and micrometer scale in a silicon crystal. Porous silicon layers may be used, e.g., as precursor to generate thick buried oxide layers for SOI (silicon-on-insulator) devices, wherein by proper control of pore density and pore microstructure, the porous silicon can accommodate the volume increase resulting from the incorporation of oxygen during oxidation. Typically porous silicon is formed below and between laterally separated crystalline regions, in which semiconductor devices are formed. Alternatively, semiconductor devices are formed in a non-porous crystalline epitaxial layer formed by epitaxy on a previously formed porous silicon layer.
There is a need for further methods of forming porous layers and buried oxide layers in silicon.